Vacuum tight waveguide transmission window having means guarding window edges from electric stress



G. HENRY-BEZY ETAL 3,101,461 TIGHT WAVEGUIDE TRANSMISSION wmnow HAVING MEANS GUARDING wmnow EDGES FROM ELECTRIC STRESS Filed Dec. 22, 1959 Aug. 20, 1963 VACUUM O) a u.

.mvamons s. HEHRY-BEZY G- KANTORO w/sz RPALLUEL BY m ATTORNEY United States Patent 3,101,461 VAQUUM TIGHT WAVEGUEDE TRANdMISSHON WINDUW HAVENG MEANS GUARDING WEN- DOW EDGES FRQM ELECTRHC STRESS Georges Henry-Rely, Gerard Kantorowiez, and Pierre Palluel, Paris, France, assignors to Qompagnie de Telegraphic Sans Fill, Paris, France Filed Dec. 22, 1959, Ser. No. 861,334 Claims priority, appiication France Han. 5, 1959 16 Claims. (6i. 333-98) The present invention relates to high-power, microwave vacuum tubes provided with an output wave guide, and more particularly to the vacuum-tight insulating windows interposed within this guide to define or delimit the evacuated enclosure.

It is known that wave guides are used to transmit the output power with high-power vacuum tubes when the power level in question compared to the wave length no longer permits the utilization for that purpose of a coaxial cable.

In order to effectively separate the vacuum enclosure from the utilization circuits, it is necessary to interpose in the wave guide a vacuum-tight partition wall which, however, is transparent to the electromagnetic waves,

usually called a window and constructed of any suitable material such as ceramic, alumina, glass, quartz, or any suitable isolating material.

In the known tubes of the prior art, this window is brazed as a subassembly on a metallic frame of suitable construction, and the subassembly, in turn, is then brazed within the wave guide. Suitable obstacles, for example, irises, permit correction of reflections introduced within the wave guide by the presence of the window and its supporting frame.

However, it has been noted in practice during operation of these prior art structures described hereinabove that these structures utilizing a subassembly support frame for the window are subject to accidents which entrain either a rupture or breakage of the window or an unbrazing of the support frame.

The principal object of the present invention is the provision of an output window for microwave vacuum tubes which is capable to sustain the existing operating conditions without breakage or unbrazing.

Accordingly, it is an object of the present invention to provide a vacuum-tight window for use in an output wave guide adapted to transmit the output energy of high-power microwave vacuum tubes which avoids the inadequacies and shortcomings of the prior art, especially as to breakage of the vacuum-tight window and the danger of an eventually loose brazed joint.

Another object of the present invention resides in the provision of an arrangement for isolating windows delimiting the evacuated space within high power microwave vacuum tubes and transparent to electromagnetic energy waves which lengthens the life of the tubes and avoids any impairment in the operation thereof due to cracks in the window that might reduce or endanger the vacuum within the tube.

T he present invention eliminates the subassembly frames heretofore used and achieves the aforementioned object by brazing the window of insulating material or the like directly to a portion of the wave guide at the periphery of the window, the wave guide itself serving to at least partially define a frame for the window and having smooth, rounded surfaces on opposite sides of the window and located closely adjacent thereto so as to prevent or reduce the impingement of wave energy upon the brazed area. Although the insulating window is brazed directly to the wave guide, the rounded surface portions adjacent the opposite faces of the window near its periphery may be formed by bent portions of the r: ice

wave guide wall or by rings having a rounded cross section and brazed to the window and to the wave guide wall at opposite faces of the window at its periphery.

The foregoing and other objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, three embodiments in accordance with the present invention and wherein:

FIGURE 1 is a partial cross-sectional view through a first embodiment of a wave guide provided with a vacuumtight window construction in accordance with the present invention,

FIGURE 2 is a partial cross-sectional view through a second embodiment of a vacuum-tight window construction in accordance with the present invention, and

FIGURE 3 is a partial longitudinal cross-sectional view through a third embodiment of a vacuum-tight window construction according to the present invention for use in output wave guides.

According to the present invention, the periphery of the insulating window material is connected by a brazed joint directly to a portion of the wave guide which at least partially defines a frame for the window and the region within which the window is brazed to the wave guide, is disposed between two smooth, rounded surfaces provided either on the wave guide walls or by parts mounted within the wave guide, these smooth, rounded surfaces being exposed at the interior of the guide and so located, with respect to the wave energy passing freely through the window, as to prevent or reduce the striking of Wave energy upon the brazed joint.

Referring now to the drawing wherein likereference numerals are used throughout the three views to designate corresponding parts, and more particularly to FIGURE 1, the insulating window is designated therein by reference numeral 1 which is mounted within a wave guide composed of two parts 2 and 3. Each of the wave guide portions 2 and 3 is provided with :a bent portion or reentrantfold 4 and '5, respectively, at the ends thereof facing each other to define a window frame formed in any suitable manner, for example, by crimping or the like. The window 1 is placed between the folds 4 and 5 and thereupon the ends of the two wave guide portions 2 and 3 are brazed together at 6 with the window 1 in place.

In FIGURE 2, the wave guide 2 is nolonger subdivided into two portions but the window 1 is placed at the interior thereof between two annular members '7 forming guard rings. The guard rings 7 may be made, for example, of nickel, copper or analogous material, and after application against the window 1 are brazed to the periphery or rim of window 1 and to the inner walls of the wave guide, the brazing joint again being designated in FIGURE 2 by reference numeral 6. In the embodiment of FIGURE 2, the guard rings together with a portion of the wave guide wall define the frame for the window.

FIGURE 3 differs from FIGURE 1 only by the fact that the dimension of the window 1 is larger than that of the wave guides 2 and 3 such that there is no longer any need to form folds 4!- and 5 in the ends of the wave guide portions as in FIGURE 1 but that it sufiices to provide enlargements or outwardly best portions 8 and 9 at the ends of the wave guides 2 and 3. The arrangement of the exteriorly bent wall portions in FIGURE 3 introduces within the wave guide fewer obstacles to the propagation of the electromagnetic energy than the arrangement of the interiorly bent or re-entrant wall portions 4 and 5 in FIGURE 1.

In each of the illustrated embodiments, a structure is provided defining a smooth, rounded surface closely adjacent to the face of the window with the smooth, rounded surface thereof diverging from the'window inwardly of 3 the Wave guide in a direction away from the brazed joint, the structure having an outer extension of the rounded surface portion brazed directly to the window. Thus, it is clear that in each of the illustrated embodiments the brazed joint is located farther from the axis of the Wave guide than the aforementioned smooth, rounded surface portions.

The arrangements of the three embodiments mentioned and described hereinabove may be applied either along the entire circumference of a circular wave guide or only along portions of the circumference of the circular wave guide, namely those where the electric high frequency field has a significant intensity or, for a rectangular wave guide, along the opposite sides which are perpendicular to the high frequency electric field corresponding to the mode of propagation chosen for the wave within the guide.

Experience based on experimental tests as well as actual operation has clearly indicated that the arrangement of the smooth, rounded surfaces formed by surfaces 4 and 5 in FIGURE 1, by guard rings 7 in FIG- URE 2., and by surfaces 8 and 9 in FIGURE 3 within the vicinity of the brazed joints 6 suppresses radically the accidents mentioned hereinabove of breakage or unbrazing, Without limiting the present invention to the correctness of any particular theory, it is believed that these accidents were due in the prior art devices to the roughnesses and irregularities of the brazed joints thereof which were subjected to a high frequency, high-intensity electric field of very great power, this field producing within the brazed joints the appearance of charges of which the instantaneous growth or progressive growth causes an are either along the faces of the window or internally in the contact resistance with the wave guide wall. This phenomenon, in turn, produces heating and the ensuing rupture or breakage of the window experienced with the prior art devices.

The arrangement of the brazed joint between two smooth rounded surfaces, according to the present invention, apparently modifies the distribution and conditions of propagation of the wave energy in the electric field up to the brazed joints in such a manner that the intensity of the field which eventually will prevail thereat is reduced so that it is no longer sufiicient to initiate the harmful discharge at the points of irregularities of the brazed joints whereas the action of the same charges on the smooth surfaces produce no harmful effect whatsoever.

While we have shown and described three embodiments in accordance with the present invention, it is understood that the same is not limited thereto but in fact is susceptible of many changes and modifications within the spirit and scope of the present invention, and we, therefore, do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim:

1. In an output wave guide for a high power microwave tube, a window of insulating vacuum-tight material located across said wave guide and brazed in a vacuumtight manner along its periphery directly to the walls thereof, and at least one metallic body having a pair of smooth rounded surface portions facing both faces of said window adjacent to at least a part of said periphery thereof, said body being electrically connected to said wave guide walls and having further surface portions brazed to said window and forming outer extensions of said rounded surface portions.

2. In an output wave guide for a high power microwave tube, a window of insulating vacuum-tight material located across said guide and brazed in a vacuumtight manner along its periphery to the walls thereof, and at least one fold in said Walls having a portion brazed to said window, said fold having a further smooth l rounded surface portion facing one face of said window over at least a part of peripheral region thereof diverging from said window inwardly of said guide in a direction away from said brazed portion.

3. In an output wave guide for a high power microwave tube, a window of insulating vacuum-tight material located across said guide and brazed in a vacuumtight manner along its periphery to the walls thereof, and a pair of essentially U-shaped folds in said walls on either side of said window, each fold having a smooth rounded surface facing respective faces of said window in the peripheral region thereof and extending radially inwardly beyond the region of brazing, each fold being provided in distinct sections of said guide, and said sections being brazed together as well as to said window.

4. In an output wave guide for a high power microwave tube, a window of insulating vacuum-tight material located across said guide and brazed in a vacuumtight manner along its periphery to the walls thereof, and at least one metallic guard ring of essentially circular cross-section, placed in said guide in electrical contact with the walls thereof and substantially in contact with said window.

5. A wave guide with a window as claimed in claim 4, wherein said guard ring is brazed to said guide walls as well as to said window periphery.

6. in an output wave guide for a high power microwave tube, a window of insulating vacuum-tight material located across said guide and brazed in a vacuumtight manner along its periphery to the walls thereof, and a pair of metallic guard rings of essentially circular cross-section placed within said wave guide in electrical contact with the walls thereof on either side of said window and substantially in contact with the respective faces thereof.

7. An output wave guide for a high power microwave tube, having a first portion of a predetermined inner size and a second portion of enlarged inner size, said two portions being interconnected by a wall portion having a smooth rounded inner surface, and a window of insulating vacuum-tight material having a size intermediate said predetermined inner size and said enlarged inner size, said window being placed across said wave guide with at least a part of the peripheral region of a face thereof facing said rounded surface, and being brazed in a vacuum-tight manner along its periphery directly to said wall portion and to said second portion.

8. A vacuum-tight seal transparent to electromagnetic waves for use in wave guides and operative to reduce the danger of cracking of the seal or loosening of the brazed joint thereof with the wave guide Walls during operation, comprising wave guide means, window means within said wave guide means, and a metal structure electrically integral with said wave guide and defining. a metallic surface having a smooth, rounded configuration, said window means being brazed to the inner walls of said wave guide means and to said structure at points farther from the axis of the wave guide means than said metallic surface having a smooth, rounded configuration.

9. A vacuum-tight seal according to claim 8, wherein said metallic surface having a smooth, rounded configuration is formed by said wave guide walls.

10. A vacuum-tight seal transparent to electromagnetic waves for use in Wave guides adapted to operate at relatively high electromagnetic power levels and constructed to reduce the danger of cracks in the seal or damage to the brazed joint, comprising wave guide means, electromagnetically transparent window means within said wave guide means, said window means being brazed to the inner walls of said wave guide means, and means forming a metallic surface having a smooth, rounded configuration disposed within the vicinity of the brazed joint and closely adjacent to a surface portion of said window means between the portion of the latter which is brazed to the wave guide means and a portion of the window through which said electromagnetic waves freely traverse.

11. A vacuum-tight seal transparent to electromagnetic waves for use in wave guides adapted to transmit electromagnetic wave energy at relatively high power levels and operative to reduce the danger of cracks in the seal or damage to the joint thereof, comprising wave guide means, window means within said wave guide means, and electrically conductive means electrically connected with said wave guide means and effectively forming a smooth, rounded configuration, a brazed joint connecting said window means to the inner walls of said Wave guide means within the vicinity of said smooth rounded configuration but outwardly thereof with respect to the path of wave energy so that said electrically conductive means protects the brazed joint from the effects of high intensity wave energy within the wave guide means.

12. A vacuum tube seal including a wave guide whose walls include bent portions thereof defining a frame in a plane extending transversely to the longitudinal axis of the wave guide, and a Window of insulating material, transparent to electromagnetic waves, in said frame, a brazed vacuum-tight joint connecting said insulating material to said frame, said guide having an interior surface portion extending from said frame to reduce the intensity at said joint of wave energy traversing freely said window.

13. A vacuum tube seal including a wave guide whose walls include bent portions thereof at one end thereof to form a frame in a plane extending transversely to the longitudinal axis of the wave guide, said bent end portions of the wave guide walls comprising a smooth, rounded surface adjacent to said frame, and a window of insulating material, transparent to electromagnetic waves, brazed by a vacuum-tight joint to said frame, said surface being exposed at the interior of the guide and so located to reduce the intensity at said joint of wave energy traversing freely said window.

14. A vacuum tube seal including a wave guide Whose walls include essentially U-shaped bent portions thereof extending toward the interior of the wave guide to form a frame in a plane extending transversely to the longitudinal axis of the wave guide and a window of insulating material, transparent to electromagnetic waves, brazed by a vacuum tight joint to said frame, said frame being exposed at the interior of the guide to reduce the. intensity at said joint of wave energy traversing freely said window.

15. A vacuum tube seal including a wave guide whose walls include bent portions thereof extending toward the interior of the wave guide at one end thereof to form a frame in a plane extending transversely to the longitudinal axis of the wave guide, said bent end portions of the wave guide walls comprising a smooth rounded surface adjacent to said frame, and a window of insulating material, transparent to electromagnetic waves, brazed by a vacuum-tight joint to said frame, said surface being exposed at the interior of the. guide and so located to reduce the intensity at said jont of wave energy traversing freely said window.

16. A vacuum tube seal including a wave guide whose walls include bent portions thereof extending toward the exterior of the wave guide at one end thereof to form a frame in a plane to the longitudinal axis of the Wave guide, said bent end portions of the wave guide walls comprising a smooth, rounded surface adjacent to said frame, and a window of insulating material, transparent to electromagnetic waves, brazed by a vacuum-tight joint to said frame, said surface being exposed at the interior of the guide and so located to reduce the intensity at said joint of wave energy traversing freely said window.

References Cited in the file of this patent UNITED STATES PATENTS 2,683,863 Curtis July 13, 1954 2,831,047 Wadey Apr. 15, 1958 2,843,795 Bondley et a1. July 15, 1958 2,883,631 Blackad der et al. Apr. 21, 1959 2,971,172 Hamilton et a1. Feb. 7, 1961 FOREIGN PATENTS 733,655 Great Britain July 13, 1955 1,036,949 Germany Aug. 21, 1958 OTHER REFERENCES Chen: Electronics, May 1954, pages -173. 

6. IN AN OUTPUT WAVE GUIDE FOR A HIGH POWER MICROWAVE TUBE, A WINDOW OF INSULATING VACUUM-TIGHT MATERIAL LOCATED ACROSS SAID GUIDE AND BRAZED IN A VACUUMTIGHT MANNER ALONG ITS PERIPHERY TO THE WALLS THEREOF, AND A PAIR OF METALLIC GUIDE RINGS OF ESSENTIALLY CIRCULAR CROSS-SECTION PLACED WITHIN SAID WAVE GUIDE IN ELECTRICAL CONTACT WITH THE WALLS THEREOF ON EITHER IN OF SAID WINDOW AND SUBSTANTIALLY IN CONTACT WITH THE RESPECTIVE FACES THEREOF. 